Engine exhaust systems sustain thermal expansion during engine warm up from their engine start size to their engine operation size. The amount of thermal expansion between exhaust system elements is a function of: material properties; engine duty cycle; and ambient temperature. In many cases engine exhaust systems have been designed with a gap between joined elements to compensation for relative thermal expansion of the joined elements. This gap is sized to maintain tolerable stress levels between joined elements for relatively high levels of thermal expansion. Exhaust systems of this design may leak through the gaps when thermal expansion is less than the relatively high level.
Engineers are designing engines to operate over a wider horsepower range for the same application and for more diverse environments than has been previously done. Over the years engineers have discovered that current engines may operate at higher horsepower output levels by increasing combustion pressures. It is this increase in combustion pressure that has lead to higher exhaust temperatures for engines. The environment that engines are required to operate in has also been a factor for engineers to consider. Having a wider range of environments requires exhaust systems to handle different thermal expansion levels. In many cases engine exhaust systems have been improved by having a larger manifold and connecting flange for assembly of manifold sections. The larger the connecting flange, the greater will be the quantity of fasteners required to maintain proper sealing. The different materials used for fasteners compared to the exhaust manifold have lead to different rates of expansion and contraction which causes manifold cracking and fastener fatigue.
Improvements in fuel systems and electronics for engines have added capabilities of operating the engine at different load levels in a relatively short time span. For example, engines operating at high load levels will have a higher exhaust temperature than engines operating at a low load level. The ability to cycle between high and low load conditions will cause thermal expansion due to the fluctuation in exhaust temperatures. In many cases compensation for thermal expansion in exhaust manifolds may be improved by using a seal in combination with the flange. Prior techniques of compensation for thermal expansion is achieved by using seal rings. The seal rings that are known in the art have a tendency to fatigue and leak over time due to the harsh operating environment.
The present invention is directed to overcoming one or more of the problems set forth above.